(1) Field of the Invention
This invention relates to an improved process for preparing 1-ethyl-6-fluoro-1,4-dihydro-7-(2,6-dimethyl-4-pyridinyl)-4-oxo-3-quinolin ecarboxylic acid, a highly potent antibacterial agent having a broad spectrum of activity, to intermediates therefor and to their preparation.
(2) Information Disclosure Statement
Lesher and Carabateas U.S. Pat. No. 3,753,993, issued Aug. 21, 1973, shows as antibacterial agents 1-alkyl-1,4-dihydro-4-oxo-7-(pyridinyl)-3-quinolinecarboxylic acids. Illustrative of these compounds is 1-ethyl-1,4-dihydro-7-(2,6-dimethyl-4-pyridinyl)-4-oxo-3-quinolinecarboxyl ic acid (Example 6A, also known as Win 35,439), which was prepared stepwise as follows: first reacting 4-(3-aminophenyl)-2,6-dimethylpyridine with diethyl ethoxymethylenemalonate to produce diethyl 3-(2,6-dimethyl-4-pyridinyl)anilinomethylenemalonate (Example 6B), next heating the latter in an eutectic mixture of diphenyl and diphenyl ether (Dowtherm A) to produce ethyl 1,4-dihydro-7-(2,6-dimethyl-4-pyridinyl)-3-quinolinecarboxylate (Example 6C) and then heating said ester with ethyl iodide in dimethylformamide in the presence of anhydrous potassium carbonate to produce 1-ethyl-1,4-dihydro-7-(2,6-dimethyl-4-pyridinyl)-4-oxo-3-quinolinecarboxyl ic acid (Example 6A). Also shown in this patent as Example 1A is 1-ethyl-1,4-dihydro-4-oxo-7-(4-pyridinyl)-3-quinolinecarboxylic acid, now known generically as rosoxacin and also as Win 35,213.
Lesher and Carabateas U.S. Pat. No. 3,907,808, issued Sept. 23, 1975, show as antibacterial agents 1-alkyl-1,4-dihydro-4-oxo-5(or 6)-(halo, lower-alkyl or lower-alkoxy)-7-(pyridinyl)-3-quinolinecarboxylic acids. Illustrative of these compounds is 7-(3,5-dicarboxy-2,6-dimethyl-4-pyridinyl)-1-ethyl-6-fluoro-1,4-dihydro-4- oxo-3-quinolinecarboxylic acid (Example 57A), which was prepared in six steps starting with 2-fluoro-5-nitrobenzaldehyde as follows: (1) a mixture containing 2-fluoro-5-nitrobenzaldehyde, methyl acetoacetate, methanol and concentrated ammonium hydroxide was refluxed to produce dimethyl 4-(2-fluoro-5-nitrophenyl)-1,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxyl ate (Example 57B); (2) oxidizing the product of Example 57B by heating it with 4N nitric acid to produce dimethyl 4-(2-fluoro-5-nitrophenyl)-2,6-dimethyl-3,5-pyridinedicarboxylate (Example 57C); (3) catalytically hydrogenating Example 57C to produce dimethyl 4-(5-amino-2-fluorophenyl)-2,6-dimethyl-3,5-pyridinedicarboxylate (Example 57D); (4) reacting Example 57D with diethyl ethoxymethylenemalonate to produce 3-(3,5-dicarbomethoxy)-2,6-dimethyl-4-pyridinyl)-4-fluoroanilinomethylenem alonate (Example 57E); (5) heating Example 57E in Dowtherm A to produce ethyl 7-(3,5-dicarbomethoxy-2,6-dimethyl-4-pyridinyl)-6-fluoro-1,4-dihydro-4-oxo -3-quinolinecarboxylate (Example 57F); and, (6) heating Example 57F with ethyl iodide in dimethylformamide in the presence of anhydrous potassium carbonate and saponifying the resulting compound to produce 7-(3,5-dicarboxy-2,6-dimethyl-4-pyridinyl)-1-ethyl-6-fluoro-1,4-dihydro-4- oxo-3-quinolinecarboxylic acid (Example 57A). Example 56F of this patent shows the conversion of 4-(2-methoxy-5-nitrophenyl)-2,6-dimethyl-3,5-pyridinedicarboxylic acid to 4-(2-methoxy-5-nitrophenyl)-2,6-dimethylpyridine by heating it in Dowtherm A. Also, Example 64C shows the conversion of 7-(3,5-dicarboxy-2,6-dimethyl-4-pyridinyl)-1-ethyl-1,4-dihydro-6-methyl-4- oxo-3-quinolinecarboxylic acid to 7-(2,6-dimethyl-4-pyridinyl)-1-ethyl-1,4-dihydro-6-methyl-4-oxo-3-quinolin ecarboxylic acid by heating it in diethyl phthalate at 240.degree.-255.degree. C.